The present invention relates to a data entry device which is connected to an electronic typewriter, electronic computer or other electronic equipment for the entry of predetermined data thereon, and more specifically to a flexible data entry keyboard having a multitude of keys, in which stationary electrodes and movable electrodes, corresponding to the individual keys, are provided on a first substrate and a flexible second substrate, respectively, so that the stationary and movable electrodes face one another through apertures in an insulating member interposed between the two substrates, whereby, upon depression of any of the keys, the flexible second substrate is deformed to bring the movable electrode corresponding to the depressed key into contact with its corresponding stationary electrode for switch activation.
A conventional keyboard of this type generally comprises a multitude of keys 55, a switch substrate assembly 61, and an elastic member formed with cup-shaped portions 63. As shown in FIG. 1, each of the keys 55 is formed of a frame 51 and a key stem 53 supported thereby for vertical slide. Movable electrodes 57 and stationary electrodes 59, each constituting a keyswitch, are arranged in the switch substrate assembly 61 in predetermined patterns corresponding to the individual keys 55. The cup-shaped portions 63, having a tactile feedback effect, individually support operating plates 53a which are arranged corresponding to the individual keys 55 and constitute part of the key stem 53 each. The switch substrate assembly 61 includes a first substrate 67, a flexible, filmy second substrate 71, and an insulating member 73 sandwiched between the first and second substrates 67 and 71. The first substrate 67 carries thereon the stationary electrodes 59 corresponding to the keys 55 and conductors 65 connecting the stationary electrodes 59. The stationary electrodes 59 and the conductors 65 are arranged in predetermined patterns. As shown in FIG. 2, the second substrate 71 is provided with the movable electrodes 57 corresponding to the stationary electrodes 59 and conductors 69 which extend straight from side to side past the centers of their corresponding movable electrodes 57, thereby connecting the electrodes 57. The insulating member 73 is formed with a number of apertures 73a which correspond in position to the stationary and movable electrodes 59 and 57 and through which the electrodes 59 and 57 are in contact with one another.
When one of the keys 55 is depressed against the resilience of its corresponding cup-shaped portion 63 of the elastic member, a pressure portion 63a, which is formed on the inner surface of the top wall of the cup-shaped portion 63, is downwardly pressed against that portion of the second substrate 71 which overlies the corresponding movable electrode 57. As the second substrate 71 is bent in this manner, the movable electrode 57 is brought into contact with the stationary electrode 59 to turn the keyswitch on. Thus, predetermined input data corresponding to the depressed key 55 is entered.
One such prior art keyboard is disclosed in, for example, U.S. Pat. No. 4,354,068.
The assignee hereof has previously proposed, in U.S. Pat. No. 4,528,428, a keyboard of this type which is provided with a curved operating surface of keys.
In the keyboard described above, however, when the key 55 is depressed as indicated by an arrow in FIG. 3, the conductors 69, which extend straight past the center of their corresponding movable electrode 57, must be bent, together with the second substrate 71, on both sides of the peripheral edge of the aperture 73a. Accordingly, the key 55 must be operated with a large force for a long stroke before the movable electrode 57 is brought into contact with the stationary electrode 59 to turn the keyswitch on, as shown in FIG. 4. Thus, it is difficult to activate the keyswitches securely and lightly, and the predetermined data cannot be entered with reliability.
These problems are attributed to the following situations or factors. First, the conductors 69, which are electrically connected to each movable electrode 57 on the flexible second substrate 71, extend on both sides of the electrode 57. When the electrode 57 is depressed in its corresponding aperture 73a upon depression of its corresponding key, it is supported by the conductors 69 on both sides thereof.
Thus, the rigidity of the conductors 69, which are formed of patterns of silver or other material printed on the flexible substrate 71, constitutes a nonnegligible hindrance to the lightness of key depression.
Secondly, the first and second substrates 67 and 71, especially the flexible second one, is closely in contact with the insulating member 73, covering the peripheral edges of the apertures 73a. When the flexible substrate 71 is deformed by key depression, therefore, it is subjected to a substantial resistance due to friction with the insulating member 73.
These factors, when put together, have a bad influence upon the flexibility of the second substrate 71 to be deformed, thus requiring an increased key force for the activation of the keyswitches. Accordingly, the pressure portion 63a of the cup-shaped portion 63, directly touched by the flexible substrate 71, would be subjected to an increased upward reaction force from the substrate 71 at the time of key depression. Thus, a longer travel or stroke of keys 55 is required for the activation of the keyswitches.